The Doctor and his companion Sarah Jane battle against some of the most
heinous foes to emerge from the outer universe: The Pescatons. The Doctor
finds himself in the capital city of London, where the population is bewildered
and trembling beneath the violent onslaught of a merciless invader.

Who or what is the mighty Zor, whose green slanting luminous eyes glare out from
the dark of night like giant emeralds? What is the powerful alien force that is
bringing Earth's civilisation to a standstill, threatening to annihilate everything
in its path?

This is the story of a dying Planet, of a Deadly Weed, and the merciless Creatures themselves. It is a Challenge to the Doctor -- a frightening
race against time...

Notes:

Two part audio story released on LP and cassette by Argo Records in 1976, and on CD by Silver Screen Records in 1991.
Reissued on double CD by BBC Audio with an bonus interview with Elisabeth Sladen (ISBN: 0 563 52764 1).

Novelised as Doctor Who - The Pescatons by Victor
Pemberton in 1991 (Target No. 153).

Episode One(drn: 22'22")

The TARDIS makes an uncomfortable landing,
as if it were drawn down by some great magnetic force. Because of this,
the Doctor has no idea where, or when, he and Sarah have arrived. The TARDIS
had materialised on an isolated, deserted beach. As the Doctor and Sarah
emerge to investigate their surroundings, the feel not only the bitter
cold, but also that they are being watched...

In reply to the Doctor's query of what month it is, Sarah
says that she thinks it is February. From this, the position of the stars,
and the wind direction, the Doctor concludes that they just might be in
England.

Sarah notices a notice board along the beach. The Doctor
shines his torch on it and they read it. "Ministry of Defence. It is dangerous
to swim from this beach at any time. Keep out." To this the Doctor remarks
that the tide so shallow, there's barely enough water to paddle. Sarah
is puzzled, then, at the reasoning of the notice board.

The Doctor notices lights in the distance on the other
side of the bay, to far to reach on foot. "Especially in this mud," Sarah
replies as she discovers something which appears to be seaweed. Sarah remarks
on its resemblance to a baby octopus, with an eye and tentacles. On closer
examination, the Doctor discover that it is comprised of some metal substance.

Not wanting to indulge the Doctor's curiosity, Sarah
implores him that they return to the TARDIS. The Doctor, ignoring the request,
bids her to listen. As she cannot hear anything, she accuses the Doctor
of trying to frighten her. Still, the Doctor is insistent that she listen.

It is soon apparent they they are not, in fact, alone.
Something is stalking them in the black night, approaching closer and closer.
As the moon emerges from behind black clouds, they catch a brief glimpse
of the creature before it attacks. Not waiting to see what their assailant
is, the Doctor and Sarah run away down the beach, the creature in pursuit.

They elude the beast and later discover that they have
arrived in the British Isles in the present day. They learn that a government
underwater expedition has vanished from the estuary bed. This expedition
was searching for a meteorite that had fallen into the sea, causing flood
damage up the River Thames. Professor Emmison, an eminent astronomer, informs
them that this is the third expedition to vanish without a trace, and that
the river is beginning to show signs of radioactive contamination. Against
the professor's most stern warnings, the Doctor goes to investigate the
estuary bed.

The Doctor makes his way down into the murky depths of
the estuary. Here there are no signs of the life that would normally make
up a healthy ecosystem. The Doctor's explorations lead him to the gigantic
cavern formed by the meteorite impact. Exploring this, the Doctor discovers
a tunnel hollowed out into the seabed. As he travels along this tunnel,
he realises that water is growing colder and darker, a sign that the tunnel
is plunging further down. The tunnel grows narrower and narrower until
it takes a turn to the right. Something unseen brushes against the Doctor's
body. It begins to capture the Doctor in a vice-like grip, starting with
his ankle.

It soon entwines his whole body, squeezing the life out
of him. He drops his sea lamp, and by the filtering light, he sees the
creature, a great living metallic weed. It continues to grip and crush
the Doctor, preparing to feed, engulfing the Doctor. But then suddenly
it stopped and disappeared into the darkness.

The Doctor regains his composure and strength, along with
his sea lamp. The sene it illuminates is a grim one. Bobbing rhythmically
with the movement of the water, dismember human bones and skeletons beg
for the help that never came.

The Doctor presses on deeper into the tunnel. Gradually
a fluorescent glow begins to illuminate the tunnel. He has reached the
resting place. Not of a meteorite, however, for it is the reaing place
a vast cylindrical, burnt out spacecraft.

The Doctor, on closer examination, notices that the surface
is covered with claw marks resulting from a life or death struggle to escape.
Suddenly, the air in his diving helmet grows thin. Pressure builds in his
throat, as if he were being strangled.

He hears the chilling sound he heard on the beach: a heart
beat. He turns his lamp to illuminate an approaching creature. One he has
seen before. His worst fears realised, he escapes the tunnel thinking
of the threat he had seen so long ago..

Sarah helps the Doctor out of the water and he warns her
of the enemy they now face: Pescatons. He describes them as cunning, ravenous
creatures. Half-human, half-fish creatures originating from the Carcariday,
the deep sea water creature like the shark. They are the most ferocious
species the Doctor has ever met, attacking and feeding on anything that
comes in their path. In response to Sarah's question to their appearance,
the Doctor describes them as having the head and body with the shape and
texture of any shark species. Teeth sharp as nails, fins like claws, they
tower over any of their human victims. They move slowly on two webbed feet.
Sarah is sceptical at the concept of fish that can build spacecraft and
travel to other planets. The Doctor informs her that the Pescatons have
developed technology far superior to any on Earth. Sarah asks where they
come from. The Doctor replies that they come from Pesca, once a planet
covered with vast oceans, now a vast wilderness. He confirms that he has
visited it before.

Experts dismiss the Doctor's findings as pure fantasy
at best and lies at worst. Despite their denial of its existence, the Pescatons
comes out of the river into the heart of London, striking fear and terror
into the inhabitants. Night falls. As the Londoners wait for the next onslaught
from the Pescaton, it retreats into a canal, visibly weakened in its search
for salt water. It emerges later in the grounds of the London Zoo, its
strength declining further, like any fish out of water. Time is running
out for the Pescaton.

The creature slumps to the ground, its heart beat fading
away to silence. Figures emerge from the shadows against the Doctor's warnings
to examine the beast. They announce that the creature is dead and more
gather around to satisfy their curiosity. The group gathered around the
creature grows until it literally engulfs it.

Without warning, the creature rears up, striking out with
unrelenting fury at the crowd around it. The crowd disperses quickly, but
not quickly enough to escape the teeth and claws of the ferocious Pescaton.
Its newfound strength rapidly decreasing, it heads towards its last and
only hope for survival: the aquarium house.

Here in the tanks it could find the salt water and food
it required. The Doctor advances cautiously into the aquarium hall to stop
this Pescaton threat. He stops and listens. Silence. The creature is lurking
somewhere, unseen. He wonders if it could have expired. Then the heart
beat of the beast. Out of the shadows at the other end of the hall, the
emerald eyes of the creature emerge. With superhuman strength, it smashes
a nearby tank, sending water and marine life onto the floor. The Doctor
tries to get away before the other tanks fall on him. And then the Pescaton
collapses to the floor, dead. Frozen with fear, the Doctor stands and watches
the creature, its flesh disintegrating before his eyes. All that is left
is the vertebra of a large fish.

Londoners return to their daily life, relieved of the
Pescaton threat. That night, however, meteorites fall one by one into the
murky River Thames...

The Pescaton invasion had begun...

Episode Two(drn: 23'34)

Reports flood in from every corner of the
globe of meteorite landings. Earth is on the brink of hostile colonisation
by the Pescatons.

The Doctor casts his mind back to his first encounter
with this alien menace...

For thousands of years, Pesca, in the constellation Pices,
had been covered with oceans. But now the planet's orbit brought it closer
to the sun, drying up the seas, destroying all marine life.

The TARDIS lands and the Doctor steps out onto hard, baked
soil. The desert-like surroundings show no sign of life, neither plant
or animal. The Doctor discovers marks of marine life on what had once been
a seashore. As the Doctor crosses a dry riverbed, the ground gives way
and he is cast into an endless chasm.

As the Doctor comes to, eyes still closed, he notices
he is completely paralysed, seemingly stretched out on the floor of some
vast cave. He listens to the relaxing sound of lapping water in the underground
reservoirs of this planet until he hears a heartbeat. His eyes pop open,
revealing that he is surrounded by creatures pulsating to the rhythm of
their own heartbeats. Above them all is a bigger creature with an oval-shaped
head too big for its metallic scale-covered body. The Doctor becomes transfixed
by its emerald eyes.

The creature speaks, informing the Doctor that they have
been waiting for him. This is Zor, leader of all Pescatons, who brought
the Doctor to their planet to help them find a new planet, as theirs is
in danger of being destroyed. The Doctor refuses and Zor locks with him
in mental battle. In this, the Doctor learns that Zor is the nervecenter
of the entire Pescaton race. The Doctor wins the battle and escapes to
the surface. As the TARDIS takes off, he has a feeling that he would meet
up with this evil race once again...

After the first wave of landings, London settles into
an uneasy calm. All the streets are deserted, leaving a constable to patrol
his empty beat. No-one is out to feed the pigeons, Snowflakes begin to
fall and settle in Trafalgar Square. The city is waiting.

A river tug makes its way to the Great Pool of London.
The attack is swift. A Pescaton rears up out of the water and rips into
the boat. The advance guard emerges from the river, all along from the
sea into the city of London itself. The streets are now filled with chaos,
people everywhere in the path of the Pescatons. All the authorities' attempts
to stop them come to naught.

Amidst this chaos, the Doctor and Sarah travel down a
back street. Sarah discovers an abandoned baby trying to return to its
mother near a shop door. The Doctor tries to talk to and is puzzled when
it doesn't reply. Sarah inform him that it cannot. She wonders why the Army,
with all its sophisticated weaponry, can't stop this alien force. The Doctor
informs her that all their weapons are useless: Pescaton skin is like steel.
Sarah begins to get agitated at the fact that London is being destroyed,
and yet there is nothing that can be done. The Doctor asks her for her
suggestions on how this could have been avoided. She replies that everyone
should have been prepared, as there are many hostile race that could attempt
this very thing.

A Pescaton appears at the end of the street. The Doctor
bids Sarah to go with the baby, but Sarah will not leave him. The creature
moves into attack, apparently towards Sarah and the baby. The Doctor tries
to gain its attention by throwing various discarded items, but to no avail.
Finally he tries song and dance. His rendition of "Hello Dolly" turns the
creature's attention to him. The Doctor manages to slip away and meets
up with Sarah later.

But something puzzles the Doctor: without their nervecenter,
Zor, the Pescatons' power is useless. Unless Zor himself is on Earth. If
so, he must be found with all due speed. Only then could the invasion be
stopped.

The first wave of attacks cease. The Pescatons retreat
to the Thames. In an attempt to do this, one creature gets trapped in the
Underground. Sarah and the Doctor decide to go after it.

As they make their way along the tunnel, the Doctor listens
to the walls for vibrations. He plays his piccolo, as he always does when
he is nervous. The creature appears behind the Doctor, and his instinct
is to flee. But Sarah has discovered something: the creature is trembling.
Ignoring the Doctor's plea to flee, Sarah bids him to play again. He does
and the creature becomes more agitated and moves off down the tunnel.

Quite unwittingly, they have found the one weakness of
the Pescatons: high pitched noise. The hunt was on for Zor, He is found
in a sewer underneath the city streets.

With the help of Professor Emerson, the Doctor sets up
high frequency sound equipment around the walls of a sewer cavity. The
Doctor waits for Zor.

The wait is not long. Zor moves close to the cavity, but
just short of the activation barrier. Zor stares into the Doctors eyes,
draining him of power. In the process of doing thing, however, Zor moves
into the activation barrier, setting off a high-pitched whine that cut
right into his brain. Zor's heart beats faster and faster until it stops.
Zor had disintegrated before the Doctor's eyes. So too, had the entire Pescaton
race. The planet of Pesca, too, is destroyed by its own sun.